One type of construction for melt-blowing dies employs a die tip having a generally triangular nose portion mounted on a die body. In such dies, the die body is provided with a distributor cavity for distributing the flow of molten polymer the full length of the die while the die tip is provided with a row of small diameter openings which extend to the extremity of the die tip through which the molten polymer is extruded directly into two converging, high velocity streams of heated gas. The fibers formed from the molten material are attenuated and separated into discrete lengths by the gas streams.
In such dies, the distributor cavity connects with a channel in the mounting face of the die tip which leads to the die openings. The present invention is concerned with one-piece die tip constructions machined from a solid block of metal. In production dies, the length of the channel in the die tip may be ten to twelve feet while the width of the channel is usually less than one-half inch. The openings through which molten material is extruded under high pressure are extremely small, on the order of 0.010 inches to 0.25 inches in diameter, and lie in a row. Typically, they may be spaced about thirty to an inch and extend the full length of the die tip through a section of metal between the bottom of the channel and the extremity of the die tip less than one-eighth of an inch in thickness. This leaves very little metal between the openings to provide mechanical strength to hold the opposite halves of the die tip together.
Mechanical strength is required to withstand the internal, outwardly directed pressure exerted by molten polymer forced into the channel from the die body and flowing to be extruded through the die openings. Heretofore, in order to strengthen the die tip, machine screws have been inserted spanning the channel and tubular spacers have been utilized in combination with the screws to hold the halves of the die tips together. Difficulties have been found with such methods of strengthening. For example, under operating conditions, the spacers can rotate, so that spacers having special shapes to streamline polymer flow cannot be held in position and the advantage of special streamlined shapes is lost. Another difficulty has been found in that the spacers, where they abut the surface of the channel at each end, form minute cavities at those junctures wherein particles of polymer can accumulate and deteriorate. Furthermore, cleaning and washing of the die tip can cause corrosion of the screws due to leakage of the liquid through the junctures between the spacers and the channels, requiring complete disassembly of the tip to avoid such corrosion.